1. Field of the Invention
This invention relates to improved impact absorbing compressible composites. These composites can be shaped into smooth compound curves and find application wherever high efficiency impact absorption is called for such as in athletic wear, in seating systems, in vehicle interior padding materials and the like.
2. Background Information
There is a well-recognized need for high performance materials for spreading or absorbing impacts. In recent years, athletes, athletic equipment manufacturers and sports medicine professionals have recognized the need for improved impact absorbing materials in athletic equipment. These materials find application as heel pads and foot sole pads in shoes to absorb the shock of foot strike and as cushioning points under football or hockey pads such as shoulder pads, thigh pads, hip pads and the like to name but a few typical applications. Similar needs may be found in seating systems and in vehicle interiors, to name but a few representative fields in which impact absorption is a major interest.
One common approach to impact absorption in the past has involved using felts or blocks of a soft padding material. Padding materials known heretofore include cotton padding, horsehair padding, foam rubber, foamed plastics, sponge rubber and the like. In these designs, the inherent resilience of the padding material is employed to absorb and disperse the applied impact. These designs have the disadvantage that they often xe2x80x9cbottom outxe2x80x9d or fully compress on severe impacts of the type regularly encountered during use such as in athletic equipment or in vehicle interiors and thus provide minimal protection. When made thicker to avoid this problem, they become cumbersome and can interfere with the design of the article being padded, and in the case of athletic equipment can interfere with the wearer""s freedom and performance.
Impact absorbers have also been proposed which employ fluid-filled bladders such as cushioning air sacks These devices rely upon the compressibility of the enclosed fluid to provide the desired shock absorbing. In some embodiments of these devices, the fluid is fully enclosed and can not escape. In others, the fluid is gradually and controllably forced out of the bladder during the impact with the rate of release being selected to prevent exhaustion of the fluid during the impact event. While effective as shock absorbers, these devices can have the failing of ballooning or otherwise expanding in one region when another region is being compressed. This can lead to discomfort or at minimum give an unnatural or unstable feel to the user. In the case of footwear, this problem can lead to an unstable foot plant with increased opportunity for injury. Another issue with this type of pad has related to problems in forming shapes based on compound curve and to retaining structural integrity with the above-described ballooning.
Representative patents in the field of shock absorbing or impact absorbing devices include U.S. Pat. No. 4,513,449, SHOCK ABSORBING ATHLETIC EQUIPMENT; U.S. Pat. No. 4,370,754, VARIABLE PRESSURE PAD; U.S. Pat. No. 4,453,271, PROTECTIVE GARMENT; U.S. Pat. No. 4,217,705, SELF-CONTAINED FLUID PRESSURE FOOT SUPPORT DEVICE, all issued to Donzis, U.S. Pat. No. 4,446,634 for FOOTWEAR HAVING IMPROVED SHOCK ABSORPTION; U.S. Pat. No. 4,397,104 for INFLATABLE SOLE-SHOE; U.S. Pat. No. 2,863,230 for CUSHIONED SOLE AND HEEL FOR SHOES; U.S. Pat. No. 4,229,889 for PRESSURIZED POROUS MATERIAL CUSHION SHOE BASE; U.S. Pat. No. 4,637,716 for METHOD FOR MAKING ELASTOMERIC SHOE SOLES; U.S. Pat. No. 4,635,384 for FOOTWEAR SOLE; U.S. Pat. No. 4,610,099 for SHOCK-ABSORBING SHOE CONSTRUCTION; and U.S. Pat. No.4,571,853 for SHOE INSERT.
It is an object of the present invention to provide an improved impact absorbing composite. It is desired that this composite provide superior shock absorbing performance and also be capable of being formed into complex compound curve shapes, be durable and hygieiic.
An improved impact absorbing composite has now been found. This composite is capable of dispersing and absorbing impacting forces with high efficiency. The composite is characterized by a structure including a flexible plastic wall (enclosure) defining an internal cavity. This flexible enclosure is made of a material that is generally impermeable to air and is capable of having its internal pressure changed. The internal cavity of the enclosure is filled with a foam core. This core is held in place by the cavity walls. Importantly, the core is intimately adhered (glued, bonded or the like) on substantially all of its external surfaces to the internal surface of the cavity. In preferred embodiments, the wall and the core are prestressed by one another. That is, the core presses out against the wall and the wall pushes in against the core. The intimate adherent contact between the foam core and the outer wall gives rise to an unexpected degree of product integrity and unexpectedly superior impact absorbing capabilities.
In preferred embodiments, the composite has a valve or fitting communicating with the cavity so that the pressure within the cavity can be altered. This permits the composite to be adjusted to accommodate varying impacts. The invention can thus include in combination such a composite together with a device for pressurizing its cavity.
Also in preferred embodiments, the foam core is an open-celled foam or a reticulated foam so that the pressure within the core is uniform. Urethane polymers have been found to be excellent for forming the cavity and the foam and are preferred materials of construction.
In other aspects, the composites of the invention can employ cores having a plurality of different foams arranged parallel or perpendicular to the impact direction. This permits differing densities and impact resistances to be present at different positions on the composite. The impact absorbers of this invention can be used in conjunction with other materials or layers including without limitation, cosmetic or hygienic overlayers, other shock-absorbing layers or the like.
In yet another aspect, this invention provides a variety of methods for fabricating these composites. All of these methods are characterized by creating an adherent bond between the foam core and the outer layer and by pressurizing the core to a value effective to provide efficient impact absorption.
One such method involves shaping the wall surface to create a cavity, sizing and shaping the foam core so as to fully fill the cavity and preferably prestress the wall and core, adhering and enclosing the core within the cavity and adjusting the pressure within the cavity to a value effective to provide efficient impact absorption.
Another fabrication method involves shaping the wall surface to create a cavity, sizing and shaping the core so as to partially fill the cavity, placing the core within the cavity forming an elastomeric foam and preferably an open-celled or reticulated foam in situ within the cavity so as to fill the space between the preshaped foam and the cavity wall and to adhere the cavity wall to the core and preferably prestress the wall and core, and adjusting the pressure within the cavity to a value effective to provide efficient impact absorption.
Yet another fabrication method involves shaping the wall surface to create a cavity, forming a cavity-wall-adherent open-celled or reticulated foam core in situ within the cavity so as to fill the cavity and preferably prestress the wall and core, and adjusting the pressure within the cavity to a value effective to provide efficient impact absorption.
A further fabrication method involves sizing and shaping the foam core, forming the outer wall in situ around and adherent to the foam core such as by shrinking a film a core-adherent material around the core or by applying a layer of uncured wall material, such as a solution of wall-forming polymer, around and adherent to the core and then curing the uncured wall material, thereby creating a cavity enclosing and preferably prestressing the core, and adjusting the pressure within the cavity to a value effective to provide efficient impact absorption.
The present shock absorbing composites can be employed in a wide range of applications. One excellent application is as heel pads and/or sole pads for shoes, especially sport shoes, where they serve to absorb foot strike impact with high efficiency.
The composites of this invention are characterized by being easily formed in compound curve forms, by being very light weight and by being hygienic. They are further characterized by being adjustable in pressure, and thus in impact cushioning capacity. This permits them to serve in a wide range of applications with widely variable impacts.